In general, polybutene is prepared by polymerizing a C4 olefin ingredient generated in a decomposition process of naphtha using a Friedel-Crafts catalyst and has a number average molecular weight (Mn) of about 300 to 5,000. As a used raw material, there is C4 raffinate-1 which is a remainder after extraction of 1,3-butadiene from a C4 raw material. Such C4 raffinate-1 includes paraffins such as isobutene and normal butane and olefins such as 1-butene, 2-butene, and isobutene. Isobutene, one olefin ingredient of the C4 raffinate-1, is included in an amount of about 30 to 50% by weight and has highest reactivity. Accordingly, generated polybutene is mainly composed of isobutene units. In addition, polybutene can be polymerized using butane-butene fraction (B-B fraction) which is a C4 mixture generated in a crude oil refinement process. Further, polybutene can be polymerized using pure isobutene which can be diluted with a butane-based solvent.
Viscosity of polybutene increases with increase in molecular weight. For example, polybutene has a viscosity of approximately 4 to 40,000 centistokes (cSt) at 100° C. In addition, polybutene is thermally cracked at a temperature of 300° C. or higher without leaving remnants behind, and is highly soluble in a lubricant or a fuel since the polybutene has a branched alkyl structure. Therefore, the polybutene is often used as an anti-scuff agent or a viscosity index improver when added to car engine oil, and also used as a detergent when mixed with a fuel in internal combustion engines for automobiles.
Because polybutene is mainly used in gluing agents, adhesives or insulating oils, high reactivity polybutene has not been favored. In recent years, however, the demands for high reactivity polybutene have risen steadily with the increasing use of the polybutene having polar groups introduced to enhance reactivity as a fuel cleaner or a lubricant additive. Thus, non-reactive polybutene (generally called and referred to as “regular polybutene” in this specification as needed) is used in gluing agents, adhesives, insulating oils, etc., while high reactivity polybutene and midrange reactivity polybutene, capable of having polar groups introduced using reactivity, are mainly used in fuel cleaners or lubricant additives. Most widely used polybutene products produced by introducing polar groups into polybutene are, for example, polyisobutenyl succinic anhydrides (PIBSA) prepared by reacting the terminal double bond of high reactivity polybutene with maleic anhydride in a thermal process, and alkyl phenols (e.g., polybutenyl phenol, etc.) prepared by the Manich reaction of phenols and midrange reactivity polybutene. These polybutene products are advantageously considered as functional polymers. Most of the lubricant additives or fuel cleaners are prepared with the PIBSA used as an intermediate. As the double bonds of the polybutene used in the preparation of PIBSA are positioned towards the end of the polybutene, the PIBSA can be produced with higher yield. But, the yield of PIBSA possibly decreases due to steric hindrance and the resultant lower reactivity in the case that the double bonds are positioned towards the interior of the polybutene and that the more alkyl groups are attached to the double bonds as substituents.
The phenomenon that a double bond is generated at a terminal of a molecule and polymerization is terminated is contrary to a general chemical reaction theory. Accordingly, so as to prepare high reactivity polybutene and midrange reactivity polybutene which are seldom generated, catalyst selection and cocatalyst system constitution are most important, and many variables such as reaction temperature or catalyst intensity should be controlled.
Prior to the advent of high reactivity polybutene, regular polybutene, that is, non-reactive polybutene has been used in the preparation of PIBSA. For enhancing the reactivity of the non-reactive polybutene, polybutene is chlorinated with chlorine gas through a chlorination reaction and reacted with maleic anhydride to yield PIBSA. Then, amines are added to the PIBSA to complete the final product. However, this method is not desirable in the economic and environmental aspects, since it costs too much due to expensive equipment used to prevent the corrosion of the reactor and uses a large quantity of a base solution to neutralize the unreacted chlorine gas. In addition, when the final product prepared by adding amines to the PIBSA with the chlorine content raised through the chlorination reaction is used as a fuel additive or the like, it may cause some problems, including corrosion of the internal combustion engine such as automobile engines, etc. and emission of chlorine as an exhaust gas. Accordingly, an improvement has been made towards the method of preparing lubricant additives or fuel cleaners using high reactivity polybutene. Such an advance of using high reactivity polybutenes in the place of non-reactive polybutenes in the lubricant additives or fuel cleaners can be considered as a process improvement that eliminates one step of the reaction and as an eco-friendly method that excludes emission of the toxic chlorine (Cl2) gas.
Non-reactive polybutene is variously used in adhesives, sealants, lubricant additives, insulating oil, etc. requiring chemical stability (non-reactive properties), thermal stability, water barrier properties, stickiness, adhesiveness, etc. Such high reactivity polybutene, midrange reactivity polybutene, and non-reactive polybutene are used according to use of each of thereof.
U.S. Pat. Nos. 4,605,808, 5,068,490, 5,191,044, 5,408,018, 5,962,604, and 6,300,444 disclose a preparation method for high reactivity polybutene that has a vinylidene content of at least 70%, more preferably at least 80%, using boron trifluoride or a complex compound of boron trifluoride in the presence of a cocatalyst, such as water, ether, alcohol, etc. U.S. Pat. No. 7,037,999 B2 describes a polybutene having a vinylidene content less than 70% and a tetra-substituted double bond content less than 10%, and its preparation method. Korean Patent No. 10-0787851 mentions the advantages of the tetra-substituted double bonds and an economically effective preparation method for polybutene and specifies a preparation method for midrange reactivity polybutene. In addition, U.S. Pat. No. 6,518,373, which suggests technology similar to the present invention, discloses a method of continuously discharging a reaction product through polymerization of isobutene which is diluted with an inactive organic solvent in the presence of boron trifluoride and a catalyst including at least one cocatalyst. Here, the solvent and isobutene, which is not converted, should be distilled and re-circulated to the polymerization reactor after separating the catalyst from or inactivating the catalyst in the discharged reaction product, followed by distillation. Here, halogen acid and impurities present in the solvent and the non-converted isobutene are removed by washing with water several times and drying. Accordingly, a raw material can be re-circulated and, at the same time, polybutene can be continuously prepared. However, so as to wash with water once or more, a tank for mixing all of the inactive organic solvent, the non-converted isobutene and water, and a settler for separating a water layer from an organic layer are required. Therefore, if the washing is performed several times, problems such as high investment costs, use of a large amount of water, etc. may occur.